This invention relates generally to casting repair and particularly to an apparatus and method for cold metal repair for casting breaks, cracks and other damage.
A great number of machines in use today rely upon cast iron parts or xe2x80x9ccastingsxe2x80x9d for strength and reliability. Cast iron is frequently selected as the preferred means of fabricating high strength machine components in a virtually endless variety of machine environments. Such cast iron fabrications include engine blocks, pump housings, manifolds, valve bodies and the like. In large industrial or commercial-type machines, the castings used in many applications are correspondingly large and costly. With all of the advantages which cast iron provides to the machine fabricator and designer, iron castings are subject to several limitations. Perhaps the most significant limitation in the attractiveness of cast iron fabrications in many large machine environments arises from the difficulty of repairing such castings in the event they become cracked, broken or otherwise damaged. In small machines, the castings used are correspondingly small and casting repair capability does not present a significant limitation. This is because small machines may usually be disassembled to completely replace a small broken casting. In some environments, even relatively modest sized machines are placed in operational environments or physically constricted areas which make disassembly of the machine for casting replacement impractical. In large machines, the size and cost of castings makes their replacement costly and difficult. In certain environments in which large machines are used, such as underground systems, the replacement of a damaged casting may be virtually impossible.
The difficulties and high costs associated with casting replacement in operating environments such as those described above create a need in the art for apparatus and methods which permit repair rather than replacement of damaged iron castings. However, a significant disadvantage associated with cast iron fabrications is the difficulty of repairing them once they are cracked or otherwise damaged. The metal structure of most cast metals does not tolerate the use of conventional metal repair techniques such as welding or brazing due to the heat associated with such repair processes. In essence, the application of heat which accompanies welding or brazing repairs alters the metal structure of the casting and creates discontinuities of the surrounding metal. These variations and discontinuities weaken the overall casting strength in the region of the repair and are, as a result, undesirable and unsatisfactory. Other systems have been tried utilizing adhesive bonding materials such as epoxys or the like. Such systems may be satisfactory for extremely limited applications but have not enjoyed general success in meeting the needs of casting repair.
In efforts to meet the need for casting repair apparatus and methods which avoid the damaging effects of heat associated with conventional welding or brazing-type processes, practitioners in the art have developed certain xe2x80x9ccold metalxe2x80x9d repair techniques which do not utilize significant heat in affecting casting repair.
U.S. Pat. No. 4,662,806 issued to Reed sets forth a Metal Lock System and Method for repairing a casting having a crack therein. The metal lock is formed of an elongated rigid member having a plurality of lobes formed from adjacent portions thereof in a generally circular cross-section. A pattern of holes is drilled into the casting, transverse to the crack and one or more elongated metal locks are forced into the transverse drilled pattern to provide a metal locking action intended to prevent the cracked portions from spreading apart. A plurality of threaded holes are then drilled along the crack in an overlapping pattern and a plurality of threaded fasteners or lacing plugs are threaded into the overlapping holes to complete the casting repair. The lacing plugs are provided with a driving head and a break-off groove formed in the fastener. The break-off groove is intended to shear and cause the head portion of the lacing plug to be broken from the threaded remainder once the lacing plug has been threaded into the casting. As a final step, the excess of the lacing plugs extending above the surrounding casting surface may be ground away.
U.S. Pat. No. 4,845,828 issued to Reed sets forth a Method for Repairing a Metal Casting having a Crack or Break Therein which utilizes apparatus of the type set forth in U.S. Pat. No. 4,662,806. The method comprises the drilling of one or more hole patterns transverse to the casting crack which are characterized by alternate large and small diameter holes. One or more correspondingly configured metal locks are embedded into the drilled hole pattern transverse to the casting crack. A plurality of tapered holes are then drilled and tapped along the casting crack in an overlapping arrangement. The drilling process is facilitated by the use of a plurality of drilling fixtures or jigs. A plurality of lacing plugs are threaded into the drilled and tapped apertures. The lacing plugs are configured to include a break away groove which causes the head portion of the lacing plug to shear and separate along the break away groove once the lacing plug is fully seated. After all metal locks and lacing plugs have been installed, the excess plug material may be removed by grinding or other processes.
While the foregoing described prior art apparatus and methods for cold metal repair of damaged castings have enjoyed some success, the environment of casting repair remains extremely demanding and repairs remain difficult. Thus, there remains a continuing need in the art for evermore improved apparatus and methods for casting repair. In particular, there remains a need for repair systems which function to more effectively draw the casting portions on each side of a crack or damaged area together to better prevent spreading of the crack and misalignment of the crack. Prior art locks have not successfully achieved this function and often actually tend to spread the casting portions adjacent the crack when the locks are installed. Furthermore, the prior art stitching pins or lacing plugs have, in many instances, failed to form a liquid-tight/gas-tight fit when installed within their threaded bores. In addition, the entire casting repair strength is, in many respects, limited to the strength of the transversely placed metal locks themselves together with the strength of the metal lock grip upon the casting portions which receive the metal lock. In prior art locks, the design of the metal locks has generally required that the lock strength be compromised to maintain grip tenacity and thus limit the overall strength of the casting repair.
Thus, there remains a continuing need in the art for an improved apparatus and method for casting repair which overcomes these limitations of the prior art systems.
Accordingly, it is a general object of the present invention to provide an improved apparatus and method for cold metal casting repair. It is a more particular object of the invention to provide an improved apparatus and method for cold metal casting repair which more securely repairs the casting damage and which draws the repaired casting portions together to provide a secure repair and prevent spreading of the crack and realignment of the cracked portion.
In accordance with the present invention, there is provided for use in repairing a cracked casting having a crack formed therein, a casting repair apparatus which comprises: at least one metal lock defining a major axis and defining a center pair of circular lobes spaced apart on each side of the major axis, a plurality of circular lobe pairs equally spaced from the center pair, and a plurality of single circular lobes each centered upon the major axis and interleaved between the circular lobe pairs in an overlapping arrangement, the center pair of circular lobes, the plurality of circular lobe pairs and the single circular lobes all having substantially equal radii of curvature; a plurality of stitching pins; and means for forming at least one metal lock recess having a shape corresponding generally to the metal lock.